Lubricating oil compositions

ABSTRACT

This invention relates to a lubricating oil composition comprising a base stock and an antioxidant comprising an oil soluble trinuclear organomolybdenum compound of the generic formula: Mo 3 S x —(Q) (1) wherein x is from 4 to 10 and Q is a core group, which may be a ligand, and at least one other compound selected from a phenolic and an aminic compound wherein the basestock has a kinematic viscosity at 100° C. (KV 100 ) from about 2 cSt to 20 cSt (2×10 −6  to 20×10 −6  m 2 /sec) and a saturates content of at least 85%. The composition has a high oxidation stability, reduced deposit formation and is capable of giving rise to good fuel economy improvement.

This invention relates to lubricating oil compositions, especiallylubricants used in internal combustion engines, comprising base oilshigh in saturates which are resistant to oxidation.

Lubricating oil compositions are used for the smooth operation ofinternal combustion engines, power transmission components includingautomatic transmissions, shock absorbers and power steering devices andgears. The engine oils for internal combustion engines in particularserve to (i) lubricate various sliding interfaces eg between the pistonring and cylinder liner, in bearings of the crank shaft and theconnecting rod, and in the valve driving mechanism including cams andvalve lifters, (ii) cool the engine, (iii) clean and disperse thecombustion products and (iv) prevent corrosion and consequent rustformation. The stringent requirements for high performance engines inrecent years has meant greater demand from lubricants used in suchengines. Lubricating oils used in such engines usually deteriorate dueto oxidation by oxygen and nitrogen oxides (NOx) formed duringcombustion of fuels and lubricants and that contained in blow-by gas inturn formed by leakage of combustion gases into the crankcase via thepiston and cylinder interface. The concentration of NOx increases in theblow-by gas with increasing demand in performance of the engine. Thedeleterious effects of oxidation can be and have been mitigated by theuse of various additives including antioxidants, anti-wear agents,ash-free detergent dispersants, friction modifiers and the like.

Hitherto these have been mitigated to some extent by the use oflubricating compositions which comprise a Group I base oil which isrelatively low in saturated hydrocarbons (hereafter “saturates”) inspite of its relatively high propensity to oxidation. Whilst this hasmeant that the base oil itself is relatively inexpensive, it has had tobe supplemented with relatively large amounts of additives/antioxidantsto achieve the desired performance. However, by using a relatively morerefined feedstock such as the Group II & Group III basestocks high insaturates, it is possible to achieve the desired performance withoutunduly supplementing the additives/antioxidants used.

It has now been found that by using a specific combination ofantioxidants, it is possible to use Group II and Group III base stockshigh in saturates with enhanced performance in respect of oxidationstability and fuel efficiency.

Accordingly, the present invention is a lubricating oil compositioncomprising a base stock and an antioxidant comprising an oil solubletrinuclear organomolybdenum compound of the generic formula:

 Mo₃S_(x)—(Q)  (I)

wherein x is from 4 to 10, preferably 7, and Q is a core group, whichmay be a ligand, and at least one other compound selected from aphenolic and an aminic compound characterised in that the base stock hasa kinematic viscosity at 100° C. (KV₁₀₀) from about 2 cSt to 20 cSt(2×10⁻⁶ to 20×10⁻⁶ m²/sec) and a saturates content of at least 85%.

The lubricating oil compositions of the present invention are those thatcomprise a major amount of a Group II or Group III base stock which maybe a natural or synthetic lubricating oil having a KV₁₀₀ of 2-20 cSt,preferably from 2-12 cSt and a saturates content of at least 85%,preferably at least 88%. Specific examples of Group II basestock high insaturates include inter alia RLOP 500R and Mobil Jurong 500N (with >97%saturates), and MXT 5 (with 92% saturates); and examples of Group IIIbasestock include inter alia Yubase 4 (with saturate contents of 99.5%)and Yubase 6 (with saturate contents of 97.5%).

According to a further embodiment, the present invention is a method ofstabilizing a lubricant composition against oxidative degradation, saidcomposition comprising a base stock which has a kinematic viscosity at100° C. (KV₁₀₀) from about 2 cSt to 20 cSt (2×10⁻⁶ to 20×10⁻⁶ m²/sec)and a saturates content of at least 85% said method comprising adding tothe basestock an effective amount of an antioxidant comprising an oilsoluble trinuclear organomolybdenum compound of the generic formula:

Mo₃S_(x)—(Q)  (I)

wherein x is from 4 to 10, preferably 7, and Q is a core group, whichmay be a ligand, and at least one other compound selected from aphenolic and an aminic compound.

The trinuclear molybdenum compounds are of formula (I)

Mo₃S_(x)—(Q)  (I)

wherein x is from 4 to 10, preferably 7, and Q is a core group. Thesecompounds are relatively new and are claimed and described in our priorpublished U.S. Pat. No. 5,906,968. The matter disclosed in this priorU.S. patent on the structure, preparation and properties of thetrinuclear molybdenum compounds is incorporated herein by reference. Inthese compounds the core group (Q) may be a ligand capable of renderingthe organomolybdenum compound of formula (I) oil soluble and ensuringthat said molybdenum compound is substantially charge neutral. The coregroup (Q) is generally associated with suitable ligands such as L,wherein L is the ligand and y is of a sufficient number, type and chargeto render the compound of formula (I) oil soluble and to neutralise thecharge on the compound of formula (I) as a whole. Thus, morespecifically, the trinuclear molybdenum compound used in thecompositions of the present invention may be represented by the formula(II):

Mo₃S_(x)L_(y)  (II)

The ligands “L” are suitably dihydrocarbyl dithiocarbamates of thestructure (—S₂CNR₂) wherein the dihydrocarbyl groups, R₂ impart oilsolubility to the molybdenum compound. In this instance, the term“hydrocarbyl” denotes a substituent having carbon atoms directlyattached to the remainder of the ligand and is predominantly hydrocarbylin character within the context of this invention. Such substituentsinclude the following:

(1) hydrocarbon substituents, ie, aliphatic (for example alkyl oralkenyl), alicyclic (for example cycloalkyl or cycloalkenyl), aromatic-,aliphatic- and alicyclic-substituted aromatic nuclei and the like, aswell as cyclic substituents wherein the ring is completed throughanother portion of the ligand (that is, any two indicated substituentsmay together form an alicyclic group);

(2) substituted hydrocarbon substituents, ie, those containingnonhydrocarbon groups which, in the context of this invention, do notalter the predominantly hydrocarbyl character of the substituent. Thoseskilled in the art will be aware of suitable groups (eg halo (especiallychloro), amino, alkoxyl, mercapto, alkylmercapto, nitro, nitroso,sulphoxy etc.); and

(3) hetero substituents, ie, substituents which, while predominantlyhydrocarbon in character within the context of this invention, containatoms other than carbon present in a chain or ring otherwise composed ofcarbon atoms.

The hydrocarbyl groups are preferably alkyl (e.g. in which the carbonatom attached to the remainder of the ligand “L” is primary, secondaryor tertiary), aryl, substituted aryl and/or ether groups.

Importantly, the hydrocarbyl groups of the ligands should be such thatthey have a sufficient number of carbon atoms to render the compound (I)soluble or dispersible in the oil to which the trinuclearorganomolybdenum compound containing the ligand is added. The totalnumber of carbon atoms present among all of the hydrocarbyl groups ofthe organomolybdenum compounds' ligands is suitably at least 21,preferably at least 25, more preferably at least 30 and even morepreferably at least 35, typically e.g., 21 to 800. For instance, thenumber of carbon atoms in each hydrocarbyl group will generally rangefrom 1 to 100, preferably from 1 to 40 and more preferably from 3 to 20.

The antioxidant in the compositions of the present invention suitablyalso include at least one other compound selected from a phenoliccompound and an aminic compound. Among the phenolic compounds, hinderedphenols are preferred.

Examples of such phenolic compounds include inter alia:

4,4′-methylene bis(2,6-di-tert-butylphenol)

4,4′-bis(2,6-di-tert-butylphenol)

4,4′-bis(2-methyl-6-tert-butylphenol)

2,2′-methylene bis(4-ethyl-6-tert-butylphenol)

2,2′-methylene bis(4-methyl-6-tert-butylphenol)

4,4′-butylidene bis(3-methyl-6-tert-butylphenol)

4,4′-isopropylidene bis(2,6-di-tert-butylphenol)

2,2′-methylene bis(4-methyl-6-nonylphenol)

2,2′-isobutylidene bis(4,6-dimethyl phenol)

2,2′-methylene bis(4-methyl-6-cyclohexylphenol)

2,6-di-tert-butyl-4-methylphenol

2,6-di-tert-butyl-4-ethylphenol and

2,4-dimethyl-6-tert-butylphenol

Specific hindered phenols which are preferred as the antioxidants may berepresented by the generic formulae (III)-(IV) below in which R₁, R₂,and R₃ are the same or different alkyl groups from 3-9 carbon atoms andx and y are integers from 1 to 4.

Suitable aminic compounds for use in the compositions of the presentinvention are diaryl amines, aryl naphthyl amines and alkyl derivativesof diaryl amines and the aryl naphthyl amines. Preferred aminicantioxidants are represented by the formulae (VII) and (VIII) whereineach of R₄ and R₅ is a hydrogen atom or represents the same or differentalkyl groups from 1-8 carbon atoms.

Specific examples of the aminic compounds that may be used in thecompositions of the present invention include inter alia:

Monoalkyldiphenyl amines such as eg monooctyldiphenyl amine andmonononyl diphenyl amine; dialkyldiphenyl amines such as eg4,4′-dibutyldiphenyl amine, 4,4′-dipentyldiphenyl amine,4,4′-dihexyldiphenyl amine, 4,4′-diheptyldiphenyl amine,4,4′-dioctyldiphenyl amine and 4,4′-dinonyldiphenyl amine;polyalkyldiphenyl amines such as eg tetra-butyldiphenyl amine,tetra-hexyldiphenyl amine, tetra-octyldiphenyl amine andtetra-nonyldiphenyl amine; the naphthylamines such as eg α-naphthylamineand phenyl-α-naphthylamine; butylpheny-α-naphthylamine,pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine,heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine andnonylphenyl-α-naphthylamine. Of these, dialkyldiphenyl amine andnaphthylamines are preferable.

In general, the antioxidant which comprises the organomolybdenumcompound in combination with a phenolic and/or an aminic compound willform a minor component of the total lubricant composition. For example,the organomolybdenum compound typically will comprise about 0.05 toabout 5.00 wt % of the total composition, preferably from 0.05 to 2.0 wt%, and more preferably from 0.1 to 0.7 wt %, i.e., the molybdenum metalis suitably present in an amount of from about 25 to 2500 ppm,preferably from about 50 to 1000 ppm, and more preferably from 100 to700 ppm, and the phenolic and/or aminic compounds about 0.10 to about3.0 wt % of the total composition.

It has also been found that if the weight ratio of organomolybdenumcompound to the phenolic and/or aminic compound in the antioxidant is inthe range of about 80:20 to about 20:80, optimum dispersancy retentioncan be achieved by these combined antioxidants of the present invention.

It is particularly preferred that the antioxidant comprises in additionto the organo molybdenum compound, a mixture of the phenols (III)-(VI)above and the diaryl amines (VII)-(VIII) in a weight ratio ranging fromabout 80:10:10 to about 10:30:60 respectively, preferably typically50:15:35 respectively.

Optionally, the antioxidants may be combined with a carrier liquid inthe form of a concentrate. The concentration of the combinedantioxidants in the concentrate may vary from 1 to 80% by weight, andwill preferably be in the range of 5 to 50% by weight.

The antioxidant combination of the present invention can be used withany of the conventional dispersants used hitherto in the lubricatingcompositions. Examples of such dispersants include inter alia thepolyalkylene succinimides, Mannich condensation products ofpolylalkylphenol-formaldehyde polyamine and boronated derivativesthereof. However, it is preferable to use ashless dispersants such asthe ashless succinimides, especially the polyisobutenyl succinimides ofa polyamine such as eg tetraethylenepentamine or its homologues,benzylamine ashless dispersants, and ester ashless dispersants. Thedispersants are generally used in the compositions of the presentinvention in an amount ranging from about 2-10% by weight based on thetotal weight of the lubricant composition, preferably from about 4-8% byweight.

A feature of the present invention is that the compositions of thepresent invention the presence of a trinuclear organo molybdenumcompound facilitates the control of deposit formation from engine oils.More specifically, formulations containing eg a contribution of 200-750ppm, preferably from 450-550 ppm of Mo metal from the trimer and anadditional contribution of from 80-100 ppm from a detergent inhibitorpackage enables the amount of deposit formed to be significantlyreduced. Adverse effects, if any, due the presence of such molybdenumcompounds in the formulation, eg copper strip corrosion, are readilymitigated by including in the formulation a corrosion inhibitor or ametal passivator. This reduction in deposit formation has been monitoredby the so-called TEOST-MHT-2 test which test is similar to theconventionally used TEOST-33 test method except that it is run at arelatively lower temperature and for a longer time. These tests areespecially designed to test the formulations for a GF-3 specification.The TEOST-33 test is carried out at temperature cycles which fluctuatefrom 200-500° C. and last for about 2 hours and results in bulkoxidation of the oil (about 100 g). In contrast, the TEOST-MHT-2 testrelates to high temperature engine deposits as measured in tests such asTU3HT and is carried out at about 285° C. over 24 hours and is athin-film test on about 8 g of oil. The TEOST-MHT-2 test measuresdeposits produced on a heated rod or in the oil itself (filteredresidue) and the GF-3 specification is envisioned to specify a limit of40 mg deposit. From the results in the Examples below it will be seenthat the presence of a trinuclear organo molybdenum compound in suchoils results in about 66% reduction in the total weight of the depositsformed which satisfies the GF-3 specification.

In general, these lubricating compositions may include additivescommonly used in lubricating oils especially crankcase lubricants, suchas antiwear agents, detergents, dispersants, rust inhibitors, viscosityindex improvers, extreme-pressure agents, friction modifiers, corrosioninhibitors, emulsifying aids, pour point depressants, anti-foams and thelike.

A feature of the present invention is that lubricant compositionscomprising high saturates base oils and trinuclear organomolybdenumcompounds in combination with a phenolic and/or an aminic compound asantioxidant provide unexpected improvement in oxidation control andsignificant benefits in fuel economy. In the case of lubricantscompositions comprising high saturates base oils for diesel engine oils,the present invention confers the added benefits of viscosity increasecontrol and dispersancy retention over compositions which contain onlyone of these antioxidants used alone.

The present invention is further illustrated with reference to thefollowing Examples:

EXAMPLES

General Procedure

A series of Test oils were prepared. These oils were then tested in abench oxidation test which was conducted at 165° C. under a mixednitrogen/air flow, with 40 ppm iron from added ferric acetylacetonate ascatalyst. The flow rates of air and nitrogen were controlled at 500ml/min and 350 ml/min respectively.

In these tests the following commercial materials have been used:

Irganox ® L57 is an octylated/butylated diphenylamine (ex Ciba Geigy)Irganox ® L101 is a high molecular weight phenolic antioxidant (ex CibaGeigy) Irganox ® L115 and Irganox ® L 1035 are high molecular weightphenolic antioxidants with a thioether group (ex Ciba Geigy) Irganox ®L06 is an alkylated phenyl-α-naphthylamine (ex Ciba Geigy) Irganox ®L135 is a high molecular weight phenolic antioxidant (ex Ciba Geigy)Irganox ® L150 is a mixture of alkylated diphenylamine, a phenolicantioxidant and a phenolic antioxidant with a thioether group (ex CibaGeigy) Paranox ® 106 is a polyisobutenylsuccinimide dispersant (exInfenium, Linden, NJ) Molyvan ® 822 is a dinuclear molybdenumdithiocarbamate containing 5% wt molybdenum (ex R T Vanderbilt Co)PDN5203 is an experimental sample of trinucler molybdenumdithiocarbamate containing 5% wt molybdenum Paratone 8451 is a viscosityindex improver (ex Oronite) Paraflow ® 390 is a pour point depressant(ex Oronite) DI is a conventional detergent inhibitor package which isfree of a friction modifier package 120X is a Group II base oilwith >92% in saturates (ex.Imperial Oil, Canada)

The same conventional DI package was used in all the Examples and tests,where indicated.

Examples A-I

Comparison Between Low and High Saturates Base Oils

The compositions of the test oils in these used in these Examples andtheir changes in respective viscosities after a 48 hour oxidation testare given in Table 1 below:

TABLE 1 Example A B C D E F G H I MCT 30 (% wt) 93.0  93.0  93.0  — — —— — — RLOP 500R (% wt) — — — 93.0  93.0  93.0  — — — Mobil Jurong 500N(% wt) — — — — — — 93.0  93.0  93.0  Paranox ® 106 (% wt) 6.0 6.0 6.06.0 6.0 6.0 6.0 6.0 6.0 Mo₃-dithiocarbamate* 1.0 — 0.5 1.0 — 0.5 1.0 —0.5 Irganox ® L57 — 1.0 0.5 — 1.0 0.5 — 1.0 0.5 Fresh Oil KV₁₀₀, cSt12.99 13.18 13.06 12.87 12.64 12.78 12.6  12.31 12.38 Used Oil Ky₁₀₀,cSt 14.3  21.66 15.54 25.03 28.76 12.87 46.25 34.6  12.59 % Increase**10.08 64.34  3.68 94.48 127.53   0.70 267.06  181.1   1.70 *containing11.5% wt of molybdenum **changes in viscosity after 48 hr oxidationtests.

From the above it can be seen that the trinuclear molybdenumdithiocarbamate and the diarylamine individually perform better in lowsaturates base oil, but, unexpectedly, a combination of the two gives abetter performance in high saturates base oils than the individualcomponents.

Examples J-O

Comparison Between a Trinuclear Molybdenum Compound and a DinuclearMolybdenum Compound

The compositions of the test oils in Examples J-Q and their respectivechanges in viscosity data after a 48-hour oxidation test on each areshown in Table 2 below:

TABLE 2 Example J K L M N O P Q MCT 30 (% wt) 93.0  93.0  93.0  93.0  —— — — RLOP 500R (% wt) — — — — 93.0  93.0  93.0  93.0  Paranox ® 106 (%wt) 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 PDN 5203 (wt %)* 1.0 — 0.5 — 1.0 —0.5 — Molyvan ® 822 (wt %) — 1.0 — 0.5 — 1.0 — 0.5 Irganox ® L57 (wt %)— — 0.5 0.5 — — 0.5 0.5 Fresh Oil KV₁₀₀, cSt 12.98 13.00 12.91 12.9712.65 12.71 12.64 12.63 Used Oil KV₁₀₀, cSt 16.19 24.94 13.59 13.9378.99 79.50 12.77 12.87 % Increase* 24.7  91.8  5.3 7.4 524    526   1.0 1.9 *changes in viscosity after 48 hr oxidation tests.

Examples J-Q show that the trinuclear molybdnum dithiocarbamate givesbetter performance than conventional dinuclear molybdenumdithiocarbamate in oxidation control. The performance of the trinuclearmolybdenum compound is further enhanced in base oils high in saturates.

Synergy of Trinuclear Molybdenum Dithiocarbamate with a Base Oil High inSaturates in the Presence of Antioxidant Mixtures

Examples R-U

The changes in viscosity after a 32 hour oxidation test in Examples R-Uis shown in Table 3 below:

TABLE 3 Example R S T U MCT 30 (% wt) 93.0 93.0 — — RLOP 500R (% wt) — —93.0 93.0 Paranox ® 106 (% wt) 6.0 6.0 6.0 6.0 Mo₃-dithiocarbamate* (%wt) 0.5 0.5 0.5 0.5 Irganox ® L57 0.5 — 0.5 — Irganox ® L150 (% wt) —0.5 — 0.5 Fresh Oil KV₁₀₀, cSt 13.39 13.41 12.73 12.78 Used Oil KV₁₀₀,cSt 13.64 13.62 12.78 12.82 % Increase** 1.87 1.57 0.39 0.31 *containing11.5% by wt molybdenum **changes in viscosity afier 48 hr oxidationtests.

Examples R-U demonstrate that mixtures of aininic and phenolicantioxidants give equivalent performance to an aminic antioxidant. Baseoils high in saturates provide additional benefit in viscosity control.

Fuel Economy Improvement

Fuel economy is measured in different types of engine tests includingthe Sequence VIA, Sequence VIB and the M111 tests. Sequence VIA and theM111 tests evaluate initial fuel economy while Sequence VIB testdetermines initial and retained fuel economy after 96 hours.

In all engine tests, fuel economy is estimated as a function of thehydrodynamic and boundary contribution of the lubricant to fuelconsumption. The lubricant contribution under hydrodynamic conditions ismostly governed by the lubricant viscometrics under both low and highshear conditions while the lubricant contributions under boundaryconditions are most governed by the friction modifier technology.

For the purpose of illustrating this invention, we concentrate on thelubricant contribution to the boundary operating range of the engine,which in the Sequence VIB test is measured in Stage 5 of that testwhereas the Sequence VIA is measured in Stage 1 of that test. Thefollowing Examples, therefore, refer to test performances in Stage 1,Stage 5 and the M111 tests as appropriate.

Example V

A 5W-20 formulation comprising a Group II base oil is shown in Table 4below:

TABLE 4 Component Weight % Component type MXT 5 79.034 Group IIbasestock Paratone ® 8452* 6.10 OCP VI Improver Parabar ® 9230** 10.50Borated PIBSA-PAM dispersant SAP 001** 2.25 Ca salicylate - 165 TBNSAP007** 0.56 Mg salicylate - 345 TBN Irganox ® L135 0.30 High M Wphenolic AOX Parabar ® 9417** 0.36 Secondary ZnDDP Paranox ® 15** 0.69Primary ZnDDP Parabar ® 10100** 0.20 Corrosion Inhibitor Parabar ®9499** 0.006 Demulsifier *Paratone ® 8452 is sold by Oronite, Richmond,California, USA **Parabar ® , Paranox ® and SAP additives are sold byInfenium, Linden, New Jersey, USA.

The fuel economy and fuel economy retention data were collected using agasoline passenger car M111 fuel economy test (CES-L54-X-94) and a M111fuel economy retention test. In the M111 fuel economy retention test,the duration of the test is extended by repeating the standard testcycles 21 times. Each test cycle is followed by a period of steady stateaging. The aging is equivalent to 500 miles. The total test is thusequivalent to about 10,000 miles, and takes about 185 hours. Fuelconsumptions are measured at every cycle, hence every 500 miles. Thefuel consumption reference RL191 is measured both at the beginning andend of the test, thereby allowing uninterrupted aging of the test oil.The effects of a trinuclear molybdenum dithiocarbamate on fuel economyand fuel economy retention are shown in Table 5 below. The initial fueleconomy improvement data are thus based on comparison with the industryreference oil RL191 (which is a 15W-40 engine oil).

TABLE 5 Integrated fuel economy improvement (vs base case) over InitialFuel 10,000 mile drain Formulation Economy / % interval / % Base case5W-20 (Table 4) 2.20 — Base case + 1.1% 2.38 10.6 Sakaralube ® 155* Basecase + 0.2% PDN 5203 2.54 34.6 Base case + 1.0% PDN 5203 2.73 36.2*Sakaralube ® 155 is a dinuclear Mo dithiocarbamate (5% wt Mo, ex AsahiDenko Kogyo KK)

Example V shows that addition of molybdenum compounds leads to betterfuel economy retention in a European gasoline passenger car engine. Theuse of trinuclear molybdenum dithiocarbamate provides significantimprovement in initial fuel economy and fuel economy retention over theconventional dinuclear molybdenum dithiocarbamate.

Example W

A 5W-20 engine oil formulation comprising a Group III base oil is shownin Table 6 below:

TABLE 6 Component Weight % Component type Yubase 6 45.4 Group IIIbasestock Yuabse 4 40.3 Group III basestock DI 8.3 DI package free offriction modifier Paratone ® 8464* 6.10 OCP VI Improver *Paratone ® 8464is sold by Oronite, Richmond, California, USA

The sequence VIA screener data in stages 1, 4 and 7 (stages sensitive tofriction modifier) using a trinuclear molybdenum dithiocarbamate on fueleconomy are shown in Table 7. The % fuel economy improvement wasmeasured versus an industry baseline calibration oil (BC-3) for SequenceVIA (BC-3 is a non-friction modified synthetic 5W-30).

TABLE 7 % Fuel Economy Improvement Formulation Stage 1 Stage 4 Stage 7Base case (Table 6) 0.612 1.804 −0.622 Base case + 1.0% PDN 5203 2.2141.998 0.854

Thus, Example W further demonstrates the benefit of trinuclearmolybdenum dithiocarbamate in fuel economy improvement in a NorthAmerican gasoline engine.

Example X

The TEOST-MHT-2 test was performed in a manner very similar to theconventional TEOST-33 test for a GF-2 specification by running at alower temperature (285° C.) but for a longer period of time ie 24 hourson an 8 g sample of oil. The test is set to measure deposits produced ona heated rod or in the oil itself (filtered residue) and it was expectedto match the currently given GF-3 specification limit of 40 mg ofdeposit. The results are tabulated in Table 8 below:

TABLE 8 Blend Components Type 5W-30 5W-30 120X (wt %) Baseoil 81.5180.51 DI (wt %) Free of friction 8.29 8.29 modifier PDN5203 Mo-trimer —1.00 Paratone ® 8451 VI improver 10.00 10.00 Paraflow ® 390 Pour pointdepressant 0.20 0.20 MHT-2 TEOST Test Filter wt (mg) 5.2 0.9 Rod wt (mg)70 26.4 Total wt (mg) 75.2 27.3

We claim:
 1. A lubricating oil composition comprising a base stock thehaving a kinematic viscosity at 100° C. (KV₁₀₀) from about 2 cSt to 20cSt (2×10⁻⁶ to 20×10⁻⁶ m²/sec) and a saturates content of at least 85%and an antioxidant comprising an oil soluble trinuclear organomolybdenumcompound of the generic formula: Mo₃S_(x)—(Q)  (I) wherein x is from 4to 10, preferably 7, and Q is a core group, which may be a ligand, and amixture of a phenolic compound of of formulae (III) to (VI):

wherein R₁, R₂, and R₃ are the same or different alkyl groups from 3-9carbon atoms and x and y are integers from 1 to 4 and of an aminiccompound of formula (VII) or (VIII):

wherein each of R₄ and R₅ is a hydrogen atom or represents the same ordifferent alkyl groups from 1-8 carbon atoms in a weight ratio rangingfrom about 80:10:10 to about 10:30:60 respectively.
 2. A compositionaccording to claim 1 wherein the basestock is a Group II or Group IIIbase stock which may be a natural or synthetic lubricating oil having aKV₁₀₀ of 2-12 cSt.
 3. A composition according to claim 1 wherein thetrinuclear molybdenum compounds are of formula (I) Mo₃S_(x)—(Q)  (I)wherein x is 7 and Q is a core group.
 4. A composition according toclaim 3 wherein the core group Q is a ligand capable of rendering theorganomolybdenum compound of formula (I) oil soluble and ensuring thatsaid molybdenum compound is substantially charge neutral.
 5. Acomposition according to claim 4 wherein the antioxidant which comprisesthe trinuclear organomolybdenum compound, the phenolic and the aminiccompound forms a minor component of the total lubricant composition. 6.A composition according to any one of claims 1, 2 or 4 wherein thetrinuclear organomolybdenum compound is present in said composition inan amount of about 0.05 to about 5.00 wt % of the total composition. 7.A composition according to claim 6 wherein the amount of phenolic andaminic compounds present in said composition is about 0.10 to about 3.0wt % of the total composition.
 8. A method of stabilizing a lubricantcomposition against oxidative degradation, said composition comprising abasestock which has a kinematic viscosity at 100° C. (KV₁₀₀) from about2 cSt to 20 cSt (2×10⁻⁶ to 20×10⁻⁶ m²/sec) and a saturates content of atleast 85% said method comprising adding to the basestock an effectiveamount of an antioxidant comprising an oil soluble trinuclearorganomolybdenum compound of the generic formula: Mo₃S_(x)—(Q)  (I)wherein x is from 4 to 10, preferably 7, and Q is a core group, whichmay be a ligand, and a mixture of a phenol of formula:

wherein R₁, R₂, and R₃ are the same or different alkyl groups from 3-9carbon atoms and x and y are integers from 1 to 4 and of an aminiccompound of formula:

wherein each of R₄ and R₅ is a hydrogen atom or represents the same ordifferent alkyl groups from 1-8 carbon atoms in a weight ratio rangingabout from 80:10:10 to about 10:30:60 respectively.
 9. A method ofimproving fuel economy of a lubricant composition, said compositioncomprising a basestock which has a kinematic viscosity at 100° C.(KV₁₀₀) from about 2 cSt to 20 cSt (2×10⁻⁶ to 20×10⁻⁶ m²/sec) and asaturates content of at least 85% said method comprising adding to thebasestock an effective amount of an antioxidant comprising an oilsoluble trinuclear organomolybdenum compound of the generic formula:Mo₃S_(x)—(Q)  (I) wherein x is from 4 to 10, preferably 7, and Q is acore group, which may be a ligand, and a mixture of a phenol of formula:

wherein R₁, R₂, and R₃ are the same or different alkyl groups from 3-9carbon atoms and x and y are integers from 1 to 4 and of an aminiccompound of formula:

wherein each of R₄ and R₅ is a hydrogen atom or represents the same ordifferent alkyl groups from 1-8 carbon atoms in a weight ratio rangingfrom about 80:10:10 to about 10:30:60 respectively.